The vehicle bus reports loss of communication with smart wastegate position sensor A. Closed-loop wastegate control loses its actual feedback; boost falls back to an open-loop fail-safe.
Medium severity. Can I keep driving?It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Most likely causes
- Bus wiring open or shorted
- Module without power or ground
- Module failed
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It can trigger limp mode.
- It affects emissions.
What each character of U0644 means
- U: Communication network
- 0: Generic code: same on every make
- 6: Subsystem depends on the code range
- 44: Specific fault in that system
Frequently asked questions
Can I keep driving with code U0644?
It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.
What causes code U0644?
The most common causes are: bus wiring open or shorted; module without power or ground; module failed.
Related codes
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.